Method for rapid and uniform heating of a multilayer assembly comprising at least one thin layer based on an ion-conducting macromolecular material interleaved between two structures with high electronic conduction

ABSTRACT

Between the high electronic conduction structures of the multilayer assembly an electric voltage signal is applied of which at least one portion includes an alternating component which has an amplitude between 0.05 and 100 volts and a frequency lower than 5 kHz and preferably between 2 and 2000 Hz so as to generate within the multilayer assembly an alternating ion current susceptible of producing a heating of the ion conducting macromolecular material by Joule effect. Application to the heating of electrochemical current generators in thin layers with solid polymer electrolyte or to the surface heating of elements of various regular or irregular shapes of which the surface is coated with the multilayer assembly.

The invention relates to a method for rapid and uniform heating of amultilayer assembly comprising at least one thin layer of anion-conducting macromolecular material, that is to say of a polymericsolid electrolyte, which is intercalated between two structures withhigh electronic conduction so as to be in intimate contact with the saidstructures.

A large class of multilayer assemblies of the abovementioned type isthat of thin-layer electrochemical current generators, rechargeable orotherwise, among which there may be mentioned the electrochemicalcurrent generators which are described in reference EP-A-0,013,199 andwhich rely on an ion-conducting macromolecular material consisting of asolid solution of an ionisable alkali metal salt M⁺ X⁻, especially alithium salt, within a plastic polymeric material made up, at leastpartially, of one or more polymers and/or copolymers of monomerscontaining at least one heteroatom, especially oxygen or nitrogen,capable of forming bonds of the donor-acceptor type with the cation M⁺.

Thin-layer electrochemical current generators make it possible to storea large quantity of energy per unit of volume and of weight. The powerwhich they can deliver depends directly on the mobility of the ions inthe ion-conducting macromolecular material, that is to say on the ionconductivity of this material.

It is known that the ion conductivity of ion-conducting macromolecularmaterials employed in thin-layer electrochemical current generators isrelatively low at temperatures below or equal to room temperature, butthat the said conductivity increases with temperature. It is thereforeuseful, when it is desired to make such generators operate at highinstantaneous power, to be able to raise their temperature rapidly and,if possible, homogeneously.

This is particularly useful for making the best use of highly energetic,essentially primary, generators which have been stored for a long timeat temperatures close to or below room temperature, which areparticularly suited to a reduction or even a complete suppression of theself-discharge phenomenon. When rapidly heated, such generators caninstantaneously supply extremely high powers even after several years'storage, provided that they can be heated rapidly and homogeneously justbefore their intensive use.

The use of an external source of heat for heating the abovementionedthin-layer current generators does not allow the required result to beobtained because operating in this way results in the appearance of atemperature gradient inside the generator, due to the poor diffusion ofheat in the multilayer structure forming the generator, and this isreflected in a nonhomogeneous operation of the generator.

It has already been proposed, as described in reference GB-A-2,065,027,to perform the heating of a polymeric composition forming a thin layerand containing an ion-conducting macromolecular material consisting of apolyether coupled with an ionisable salt by relying on a heatingtechnique using dielectric losses, which consists in subjecting the saidcomposition to the action of electromagnetic waves of very highfrequencies, namely frequencies of the order of 10⁶ to 10⁸ hertz.

Such a heating technique using dielectric losses is not suitable forheating thin-layer electrochemical current generators such as referredto above, or more generally for heating assemblies comprising at leastone thin layer of an ion-conducting macromolecular material sandwichedbetween two structures with high electronic conduction because, apartfrom the difficulties linked with its implementation and thedisadvantages which it entails for the environment owing to the use ofelectrical signals of very high frequency, this technique does not lenditself well to heating multilayer structures comprising a number oflayers with high electronic conduction which are close to each other.

The subject of the invention is a method of rapid and uniform heating ofa multilayer assembly comprising at least one thin layer of anion-conducting macromolecular material intercalated between twostructures with high electronic conduction so as to be in intimatecontact with the said structures, which makes it possible to overcomethe disadvantages of the methods of heating using an external source ofheating or using dielectric losses.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawing, wherein:

the FIGURE shows an embodiment of the multilayer assembly of theinvention of a macromolecular material sandwiched between twoelectrodes.

The method according to the invention is characterised in that betweenthe structures with electronic conduction which are situated on bothsides of each layer of ion-conducting macromolecular material anelectrical voltage signal is applied, at least part of which comprisesan alternating component which has a frequency of less than 5 kHz and anamplitude, that is to say a difference between its maximum and meanvalues, of between 0.05 and 100 volts, so as to generate in themultilayer assembly an alternating ion current capable of producing aheating of the ion-conducting macromolecular material by Joule effect.

The frequency of the alternating component of the electrical voltagesignal applied between the structures with electronic conduction isadvantageously more particularly between 2 and 2000 Hz and is preferablybetween 10 and 500 Hz. In addition, the preferred values of theamplitude of the said alternating component are between 0.05 and 30volts.

The alternating component of the electrical voltage signal employedaccording to the invention may be sinusoidal or nonsinusoidal and may beuninterrupted or noncontinuous.

This alternating component may consist especially of a sinusoidalelectrical voltage of a frequency equal to 50 or 60 Hz, generated by thesinusoidal alternating voltage supplied by the electricity supplysystems.

A person skilled in the art will be easily capable of adjusting theelectrical power to be supplied to the terminals of any multilayerassembly of the abovementioned type with a polymeric solid electrolyte,which it is desired to heat, to reach the desired temperature in aspecified time by taking into account the size and the geometry of thesaid multilayer assembly to be heated, its heat capacity and its heatloss to the external environment.

In fact, the heat power dissipated in the polymeric solid electrolytebecause of the alternating motion of the ions which it contains is ofthe form U_(A) ² /Ri, U_(A) being the effective value of the alternatingcomponent of the electrical voltage signal applied and Ri denoting theion resistance of the layer of polymeric solid electrolyte of themultilayer assembly to be heated. This same ion resistance is given bythe relationship Ri=K×t/S, in which K is the ionic resistivity of thepolymeric solid electrolyte and t and S denote the thickness and thesurface area respectively of the layer of polymeric solid electrolyte ofthe multilayer assembly. The heat power dissipated in the polymericsolid electrolyte is therefore of the form U_(A) ² /Ri or K×U_(A) ²×S/t.

The alternating voltage to be applied to a multilayer assembly in orderto heat it with a given heat power is therefore proportionally lower thegreater the surface area and the smaller the thickness of this assembly.Similarly, heating a system of n identical multilayer assembly requiresthe application of an alternating voltage which is higher (coupled witha lower intensity) when these n elements are connected in series thanwhen these n elements are connected in a parallel configuration.

When the multilayer assembly is being heated, the intensity of thealternating current which is generated within the ion-conductingmacromolecular material as a result of the application of the electricalvoltage signal with an alternating component between the structures withelectronic conduction tends to increase with temperature because of thedecrease in the resistance of the ion-conducting material. If need be,the temperature within the said ion-conducting material can be monitoredwhen the multilayer assembly is being heated in order not to exceed apredetermined value, it being possible for the said monitoring to becarried out either by employing an electrical voltage signal whosealternating component has a constant effective value and by limiting theintensity of the alternating current generated or else by keepingconstant the intensity of the alternating current flowing in theion-conducting material and by limiting the amplitude of the alternatingcomponent of the electrical voltage signal. These techniques of thermalcontrol of the temperature of a conductor are well-known in the art andwill not therefore be described in detail.

The FIGURE shows a multilayer assembly embodiment of the presentinvention in which an ion conducting macromolecular material 10 isintercalated between two highly electrically conducting layers 12 and14.

A "thin layer" of the ion-conducting macromolecular material means alayer of the said material whose thickness which actually corresponds tothe distance separating the two structures with high electronicconduction situated on both side of the ion-conducting macromolecularmaterial, is low in relation to the areas of contact of thismacromolecular material with the adjacent layers formed by thestructures with high electronic conduction. The thickness of the thinlayer of ion-conducting macromolecular material is advantageouslybetween 5 μm and 2000 μm, it being necessary for the said thickness tobe as uniform as possible.

The ion-conducting macromolecular material may be any one of thepolymer-based materials capable of simultaneously having an ionconductivity of at least 10⁻⁷ siemens/cm at room temperature and anelectronic conductivity of less than 10⁻¹⁰ siemens/cm.

The ion-conducting macromolecular material may, in particular, consistof a solid solution of at least one ionisable salt, especially an alkalimetal salt and in particular a lithium salt, in a plastic polymericmaterial made up at least partly of one or more polymers and/orcopolymers of monomers containing at least one heteroatom, especiallyoxygen or nitrogen, capable of forming bonds of the donor/acceptor typewith the cation of the ionisable salt, the said polymer(s) being chosenin particular from polyethers and especially from ethylene oxide orpropylene oxide homopolymers (cf. EP-A-0,013,199). In the improvementsmade to the solid solutions of the abovementioned type the plasticpolymeric material may consist in particular of a copolymer of ethyleneoxide and of at least one other cyclic oxide, the said copolymer havingeither the structure of a random copolymer (U.S.-A-4,578,326) which maybe optionally crosslinked (FR-A-2,570,224) or else the form of a networkof the urethane type resulting from the reaction of a block copolymer ofethylene oxide and of at least one other cyclic oxide with a couplingagent consisting of an organic polyisocyanate (FR-A-2,485,274). Inaddition, the ionisable salts mentioned in reference EP-A-0,013,199 maybe partly or wholly replaced by ionisable salts such as alkali metalcholoroboranes (FR-A-2,523,770), alkali metaltetrakistrialkylsiloxyalanates (FR-A-2,527,611), alkalimetalbis(perhaloalkylsulfonyl)imides or bis(perhaloacyl)imides(FR-A-2,527,602), alkali metal tetraalkynylborates or aluminates(FR-A-2,527,610), alkali metal derivatives ofperhaloalkylsulphonylmethane or perhaloacylmethane compounds(FR-A-2,606,218) or else alkali metal salts of polyethoxylated anions(EP-A-0,213,985).

The ion-conducting macromolecular material may further consist of asolid solution of an ionisable salt, for example a salt such asdescribed in the abovementioned references, in a polymeric materialconsisting of an organometallic polymer in which at least two polyetherchains are linked by a metal atom chosen from Al, Zn and Mg(FR-A-2,557,735) or from Si, Cd, B and Ti (FR-A-2,565,413) or else of apolymeric material consisting of a polyphosphazene carrying twopolyether groups such as polyoxyethylene groups on each phosphorus atom.

The ion-conducting macromolecular material can also be chosen frommixtures of polymers of polar nature and/or solvating with any salt,acid or base which is sufficiently dissociated in the polymer to obtainthe appropriate ion conductivity or else from polymers carryingionisable functional groups producing anions or cations attached to themacromolecular chains or else from protonic conductors such as thosedescribed in reference FR-A-2,593,328 or mixtures of inert polymers withinorganic or organic ion-conducting materials dispersed in the polymericmatrix.

A structure with high electronic conduction means, according to theinvention any composite material capable of reaching electronicconductivities higher than 10⁻⁸ siemens/cm. These may be the variousmaterials generally employed as electrode collectors, that is to say inparticular films, tapes or plates of a conductive metal such as Cu, Al,Ag, Ni, Zn or else of an organic material such as polyacetylene,polypyrrole, polyanilines or any other unsaturated polymer whether dopedor not with ionic compounds. These may also be insulating materials suchas glasses or plastics coated with conductive deposits, the saiddeposits being produced by various methods such as metallisation,chemical deposition in vacuum, cathodic sputtering or lamination.

The structure with electronic conduction may also consist of a compositematerial in which at least one of the components exhibits a sufficientelectronic conductivity and, by way of examples, there may be mentionedcertain composite electrodes, especially those described in referenceEP-A-0,013,199, which couple a substance with electronic conduction suchas carbon black with various electrochemically active materials, suchelectrodes being employed especially in primary or secondaryelectrochemical current generators with polymeric solid electrolyte inthe form of thin layers.

As indicated above, the method according to the invention can be appliedin particular to the heating of multilayer assemblies consisting ofrechargeable or nonrechargeable electrochemical current generators whichconsist of at least one thin layer of a polymeric solid electrolyte,that is to say of an ion-conducting macromolecular material such asdefined above, sandwiched between two electrodes, which form thestructures with high electronic conduction and may have any suitablearrangement and in particular the composite electrode arrangementdescribed in the references which are quoted above.

The electrochemical current generators of the abovementioned type can beemployed especially for feeding electric motors fitted to variousportable pieces of equipment such as drills, vacuum cleaners, hedgetrimmers, lawnmowers and, as a result of their flexible configuration,they can be arranged in contact with the electric motors which theyfeed, and this makes it possible to produce pieces of equipment withbuilt-in current generators. In such applications of the above-mentionedcurrent generators as built-in generators, after the generator has beenheated throughout to the most appropriate temperature for its operationby making use of the heating method according to the invention, the heatgenerated, inter alia by the heat loss of the electric motor of thepiece of equipment fed by the generator, is sufficient, on conditionthat the heat management of the system is monitored, to maintain thegenerator which is fitted close to the motor in a temperature rangeenabling the said generator to operate under optimum conditions. Forexample, a sufficient number of current generators with a polymericsolid electrolyte in the form of thin layers can be arranged around theelectric motor of a lawnmower to form a battery providing apredetermined independent operation for, for example, two to threehours. By heating the generators throughout, using the method accordingto the invention, when they are being recharged, if they arerechargeable, or/and just before they are used, more than 80% of thenominal capacity of the battery can be available during thepredetermined period of operation.

In the case of a thin-layer electrochemical current generator such asmentioned above of the non-rechargeable type, the stage of heating thesaid generator by applying the method according to the invention can beperformed before the generator is used or at the beginning of the saiduse.

The electrical voltage applied to the nonrechargeable generator isadvantageously the sum of an alternating component such as defined aboveand of a direct voltage whose value is at least equal to theopen-circuit voltage of the said generator, it being possible for thesaid alternating and direct voltages to be applied simultaneously andseparately or else in the form of a single voltage resulting from theirsum.

In the case of a thin-layer electrochemical current generator such asmentioned above of the rechargeable type, the stage of heating thisgenerator using the method according to the invention can be carried outeither as shown above for a nonrechargeable thin-layer electrochemicalcurrent generator and/or during at least a part of the recharging cycleof the generator. In the case of a heating performed during therecharging cycle of the generator, the electrical voltage applied to thegenerator to be recharged is advantageously the sum of a voltage oralternating component such as defined above and of a direct electricalvoltage whose value is at least equal to the nominal voltage of thecharged generator, it being possible for the said alternating and directvoltages to be applied simultaneously and separately or else in the formof a single voltage resulting from their sum. The heating of thegenerator during the recharging cycles makes it possible to shorten therecharging time substantially.

When a number of thin-layer electrochemical current generators of theabovementioned type are combined to form the current generator, at leastone of the said unit generators can be used to produce, alternately ifnecessary, the alternating voltage which can be employed for heating theother unit generators.

The method according to the invention can also be applied to the surfaceheating of units of various shapes, whose surface is provided with amultilayer assembly comprising a thin layer of a polymeric solidelectrolyte consisting of an ion-conducting macromolecular material suchas defined above intercalated between two electrically conductive layersforming structures with high electronic conduction as shown above, thevoltage applied between the said structures being purely alternating inthis case.

It is thus possible to produce domestic heating systems using radiantpanels, for which it is known that they simultaneously permit animproved comfort and substantial energy savings. For example, in anapplication of this type the multilayer assembly can be produced in theform of a heating tapestry obtained by bonding to a sheet of metallisedpaper, which can be glued onto walls and partitions like an ordinarywallpaper, a thin layer of ion-conducting macromolecular material andthen a layer of a material which is also a good electronic conductorsuch as, for example, a second sheet of metallised paper or plastic or athin sheet of an electronically conductive metal. This heatingtechnique, which relies on the method according to the invention, offersa number of advantages, among which may be mentioned the use of very lowvoltages devoid of danger in the case of a domestic use, the ability towithstand partial tearing of the heating wall-covering without modifyingits nominal power, the possibility of piercing and nailing withoutdanger, because the short circuit which is temporarily created resultsin the local destruction of one of the conductive coatings with naturallocal healing by the ion-conducting macromolecular material (polymericsolid electrolyte), the proportion of surface which is destroyed beingnegligible compared with the total area of the multilayer assemblyforming the heating wall-covering.

When the unit to be heated at the surface has a nonuniform surface, themultilayer assembly is produced on the surface of the said unit usingpainting techniques by operating, for example, as follows. First of all,a layer of an electronically conductive material chosen from metalpowders, carbon black and conductive polymers, especially polymersbearing conjugated unsaturated bonds such as mentioned above isdeposited onto the said surface, for example in a solvent phase or byelectrostatic spraying with a gun, and on the conductive surface thusproduced a small region is kept aside, which will be protected fromcoating by the following layers and which is intended for making contactwith the electrode formed by the layer of electronically conductivematerial thus formed. A second thin layer of ion-conductingmacromolecular material is then deposited onto the layer ofelectronically conductive material by any suitable technique, forexample spraying with a gun, soaking or spreading. Finally, a thirdlayer of an electronically conductive material such as shown above isdeposited onto this second layer, this third layer acting as a secondelectrode. A region allowing an electrical connection to be made withthe source of alternating voltage is arranged in this layer, it beingpossible to make the said connection, for example, by welding or localapplication of a conductive paste such as, especially, a silver-filledepoxy resin. The deposition of the first conductive layer onto thesurface of the unit to be heated at the surface can be avoided when thesaid surface already has a sufficient electronic conductivity to act asa first electrode.

The alternating voltage which can be employed to produce the heating ofthe multilayer assembly can be generated by any known source ofalternating voltage capable of delivering an alternating electricalvoltage which has the form of an uninterrupted signal or of a pulsedsignal exhibiting the frequency and amplitude characteristics definedabove. When the multilayer assembly is of the current-generator type thesource of alternating voltage can be integrated into the said generatoror else into the apparatus employing this generator or, furthermore,into the charger employed for recharging the generator.

The following examples are given to illustrate the invention without anylimitation being implied.

EXAMPLE 1

In order to demonstrate the reversibility of the phenomena involved inthe application of the method according to the invention, a 4-cm² devicewas produced by placing in contact, on each of the faces of a 50-μmthick film of polymeric solid electrolyte, a 20-μm thick compositeelectrode made of acetylene black dispersed in a polymeric solidelectrolyte of the same kind as that of the film, the said electrodebeing carried by a 25-μm thick aluminium foil. The polymeric solidelectrolyte consisted of a solid solution of lithium perchlorate in acopolymer of ethylene oxide and of methyl glycidyl ether, the saidcopolymer containing 90 mol % of ethylene oxide and the said solidsolution having a molar ratio of oxygen atoms of the ether functionalgroups to the lithium ions whose value was approximately 20.

The device thus formed, whose e.m.f. was initially 0 volts and thetemperature was 23° C. was insulated thermally and placed in contactwith a miniaturised thermocouple to make it possible to follow rapidlyany heat effect generated. The electrode collectors were connected tothe terminals of a potentiometer operating at 60 cycles/second andcontrolled at 10-volt output. As soon as the potentiometer was switchedon the temperature rose rapidly to reach approximately 60° C. afterapproximately 30 seconds. The test was repeated a number of times andthe same effect was observed. When the potentiometer was controlled at20 volts the abovementioned temperature was reached after approximately10 seconds and the alternating current observed changed fromapproximately 60 mA to approximately 150-200 mA. When the alternatingsignal was maintained for longer than the times shown above the currenttended to increase as a result of a decrease in the internal resistanceof the device. When the e.m.f. was checked after these various tests thevoltage observed was still 0 volts. This, together with the internalresistance which remains unchanged at 24° C., confirms that the effectsare reversible and that no permanent damage was produced. The powerdissipated in a device of this kind was therefore of the order of 0.6watts for an area employed of approximately 4 cm².

EXAMPLE 2

A thin-layer lithium current generator was produced, consisting of alayer of a polymeric solid electrolyte sandwiched between a positiveelectrode and a negative electrode.

The layer of polymeric solid electrolyte had a thickness of 40 μm andconsisted of a solid solution containing 10% by weight of lithiumperchlorate in a copolymer of ethylene oxide and of methyl glycidylether, the said copolymer containing 80% of ethylene oxide by weight.

The positive electrode resulted from the agglomeration, into ahomogeneous mass, of titanium sulphide powder, of carbon black and of apolymeric solid electrolyte consisting of the abovementioned solidsolution, so as to have a lithium content over the electrodecorresponding to 4 coulombs/cm², that is approximately 0.29 mg/cm² oflithium, the said electrode being deposited onto a collector consistingof an aluminium foil of 20-μm thickness.

The negative electrode consisted of a 20-μm thick lithium foil laminatedonto a current collector consisting of a 12-μm thick copper foil.

The generator assembly, 20 cm² in area, was sealed in a flexiblemetal-and-plastic package based on laminated thin foils of polyester,aluminium and polyethylene. This package makes it possible at the sametime to make contact with the positive and negative electrodes and actsas a barrier material against water and oxygen, allowing the generatorto operate for many charge-discharge cycles.

The generator thus constituted had a mean voltage of 2.1 volts whichchanged from 3.5 to 1.6 volts during normal discharge and it made itpossible to obtain a correct use of the installed electrical capacityequal to 80 coulombs, which corresponds to 22.2 milliampere-hours forany discharge rate lower than 2 milliamperes, that is for any dischargeof the generator over a period longer than 10 hours. When producinggenerator discharges consuming more current, a rapid fall was observedin the proportion of utilisation of the electrical capacity of the saidgenerator, only 50% of which could be used any longer for a discharge at4 milliamperes, 20% for a discharge at 10 milliamperes and 5% for adischarge at 20 milliamperes.

An electrical voltage signal resulting from the superposition of analternating voltage with an amplitude of 3 volts and a frequency of 50hertz and of a direct voltage equal to 2.5 volts was applied to thegenerator produced as indicated above, before subjecting it to adischarge, the operation being carried out so that the positive terminalof the generator was connected to the alternating phase of higher meanvoltage. After a few minutes the application of the said alternatingvoltage resulted in a temperature rise of the generator from 22° C. to60° C. From then on the generator could produce a mean current of 8milliamperes corresponding to a total discharge over 2 hours (C/2). Whenhaving available a sufficient insulation or thermal inertia to maintainthe generator at a temperature above 30° C., such a current could bemaintained for about a hundred minutes (that is approximately 80% of thetotal capacity of the generator). Without producing the heatingaccording to the invention, the use of the generator at the samedischarge rate at room temperature lasted only approximately 20 minutesin the case of a final voltage of 1.6 volts, which corresponds to autilisation of less than 15% of the generator's capacity.

EXAMPLE 3

The generator as described in Example 2 required a recharging period ofat least ten hours at a constant rate of 2.2 milliamperes to obtain acomplete recharge, at room temperature, to its capacity C, equal to 4coulombs/cm². When a more rapid recharge was imposed at 25° C. by theuse of a higher intensity while the maximum recharge voltage thresholdwas maintained at 3.5 volts, a faster rise in this voltage was observedat the end of charging, corresponding to the end of the possiblerecharge, resulting in a smaller quantity of stored energy.

In other words, there is a limitation to recharge rates lower than orequal to C/10 if it is desired to achieve complete recharges at roomtemperature without damage.

The discharged generator was subjected to an alternating signal whichhad a frequency of 50 hertz and an amplitude of 4 volts superposed on adirect voltage equal to the discharged generator's own voltage. A rapidrise in temperature to about 50°-60° C. was observed, and this then madeit possible to recharge the generator fully at rates which were fivetimes faster over a period which was five times shorter than when thegenerator is kept at room temperature. It was thus possible to performthe complete recharging of the generator in two hours by applying a meanintensity of 11 milliamperes after heating, whereas this could beperformed only in at least 10 hours at room temperature.

Results which were comparable to the abovementioned results according tothe invention were obtained by subjecting the discharged generator to arecharge by making use of a potentiostatic charger (constant-voltagecharger), which applied between the electrodes of the generator anelectrical voltage signal resulting from the superposition of theabovementioned alternating voltage with an amplitude of 4 volts and afrequency of 50 hertz on the direct recharging voltage fixed at 3.5volts.

EXAMPLE 4

Heating wall coverings were produced by combining a 150-μm thick papersheet metallised on one face with a 1 to 20-μm thickness of copper, alayer of a polymeric solid electrolyte which had a thickness of between5 μm and 100 μm, the said electrolyte consisting of a solid solutioncontaining 10% by weight of KSCN dissolved in a copolymer of ethyleneoxide and of butylene oxide containing 70% by weight of ethylene oxide,and a 20-μm thick polypropylene foil metallised on one face by vacuumdeposition of a very fine layer of a good conductor metal such ascopper, so as to constitute multilayer assemblies in which the layer ofpolymeric solid electrolyte was arranged between the two metallisedsheets and adhered strongly to the metal deposit present on each of thesaid sheets.

Bonding of the layer of polymeric solid electrolyte in contact with themetal deposits present on the metallised sheets was produced by coatingthe layer of electrolyte onto the metallised paper, the operation beingcarried out by melt extrusion or else by coating with a solution of thesalt and of the copolymer in a common solvent and evaporation of thesaid solvent to form a metallised paper/polymeric solid electrolytecomposite and then by laminating the said composite with the metallisedpolypropylene foil, these operations being carried out so that in placeseach of the metal deposits facing the electrolyte layer overlapsslightly the area in contact with the electrolyte to form a small flapof free metal conductor overlapping the multilayer assembly obtained.The multilayer assemblies formed as described above were glued, on thepaper sheet side, onto plaster panels to form radiant panels.

In the case of each of the panels thus obtained an alternating voltagewith an amplitude of between 5 and 20 volts and a frequency ranging from10 to 100 hertz, depending on the test, was applied between the metalconductive deposits of the multilayer assembly of the panel in question,by means of the associated small flaps, and a rapid rise was observed inthe temperature of the multilayer assembly which dissipated the heatresulting from this temperature rise into the surrounding environment.

The dissipated power, which corresponds to the product of the currentsupplied at a given voltage, multiplied by the said voltage, dependsdirectly on the applied voltage.

This current is proportional to the area of the heating coating, to theion conductivity of the polymeric solid electrolyte and inverselyproportional to the thickness of the said electrolyte. The powerdissipated generally has values of less than 0.05 watts per cm², that is5 milliamperes per cm² for an alternating voltage of 10 volts.

The temperature rise on heating depends on the electrical powerdissipated by Joule effect and on the heat capacity and the thermalconductivity of the support onto which the heating multilayer assemblyis attached.

The heating coatings can also be produced in the form of transparentmultilayer assemblies in which a layer of a polymeric solid electrolytesuch as defined above and transparent in the layer thicknesses which areemployed is sandwiched between two transparent current-collectingsupports, each consisting of a transparent foil carrying acurrent-conducting transparent deposit on its side facing the polymericsolid electrolyte, the said layer of polymeric solid electrolyteadhering strongly to the transparent conductive deposit of each of thesaid current-collecting supports. These transparent current-collectingsupports can be obtained, for example, by vacuum deposition of very finelayers of metal oxides of the mixed tin and indium oxide type(abbreviated to ITO) or else tin oxide doped onto transparent films of aplastic substance, especially polypropylene- or polyester-based films.The polymeric solid electrolyte may advantageously consist of a solidsolution of at least one ionisable salt in a polymeric material made upat least partially of one or more copolymers of ethylene oxide and of atleast one other cyclic ether.

Such heating coatings, which are capable of being heated by theapplication of an alternating voltage according to the invention betweenthe conductive deposits of the current collectors arranged on both sidesof the layer of polymeric solid electrolyte, can be applied, for exampleby adhesive bonding, onto supporting optical systems such as domestic ormotor vehicle windows, rearview mirrors, mirrors or, further, variousluminous signalling systems, to provide the said optical systems withheating for the purpose of defrosting and/or demisting withoutappreciable detriment to the optical properties specific to theseoptical systems. The combination of the supporting optical system,especially a transparent support such as a window, or a reflectingsupport, especially a rear view-mirror or mirror, and of the heatingtransparent coating constitutes an assembly which can be described as acontrolled-temperature optical system.

We claim:
 1. A method for rapidly and uniformly heating a multilayerassembly comprising at least one thin layer of an ion-conductingmacromolecular material, intercalated between two structures having highelectronic conduction so as to be in intimate contact with the saidstructures, which comprises:applying an electrical voltage between thestructures with high electronic conduction which are situated on eitherside of each layer of ion-conducting macromolecular material, at least apart of the voltage comprising an alternating component which has afrequency of less than 5 kHz and an amplitude of between 0.05 and 100volts, so as to generate in the multilayer assembly an alternating ioncurrent capable of effecting heating of the ion-conductingmacromolecular material by the Joule effect.
 2. The method according toclaim 1 wherein the amplitude of the alternating component of theelectrical voltage signal applied between the structures with highelectronic conduction ranges from 0.05 to 30 volts.
 3. The methodaccording to claim 1, wherein the alternating component of voltage is anuninterrupted signal which is a sinusoidal signal or a noncontinuoussignal.
 4. The method according to claim 1, wherein the thin layer ofion-conducting macromolecular material of the multilayer assembly has athickness ranging from 5 μm to 2,000 μm.
 5. The method according toclaim 1, wherein the ion-conducting macromolecular material hassimultaneously an ion conductivity of at least 10⁻⁷ siemens/cm at roomtemperature and an electronic conductivity of less than 10⁻¹⁰siemens/cm.
 6. The method according to claim 5, wherein theion-conducting macromolecular material consists of a solid solution ofat least one ionizable alkali metal salt, in a plastic polymericmaterial made up at least partly of one or more polymers and/orcopolymers of monomers containing at least one heteroatom, capable offorming bonds of the donor/acceptor type with the cation of theionizable salt.
 7. The method according to claim 5, wherein theion-conducting macromolecular material consists of a solid solution ofan ionizable salt in a polymer selected from the group consisting oforganometallic polymers in which at least two polyether chains arelinked by a metal atom selected from the group consisting of Al, Zn, Mg,Si, Cd, B and Ti and from polyphosphazenes carrying two polyether groupson each phosphorus atom.
 8. The method according to claim 5, wherein theion-conducting macromolecular material is selected from the groupconsisting of mixtures of polymers of polar nature and/or solvating withany salt, acid or base which is sufficiently dissociated in the polymerto obtain the desired ion conductivity, polymers carrying ionizablefunctional groups producing anions or cations attached to themacromolecular chains, polymeric protonic conductors and mixtures ofinert polymers with inorganic or organic ion-conducting materialsdispersed in the polymeric matrix.
 9. The method according to claim 1,wherein the structures with electronic conduction are made of materialsexhibiting electronic conductivities higher than 10⁻⁸ siemens/cm. 10.The method according to claim 1, wherein the multilayer assemblysubjected to heating consists of a rechargeable or nonrechargeableelectrochemical current generator which consists of at least one thinlayer of the ion-containing macromolecular material, or polymeric solidelectrolyte, sandwiched between two electrodes which form the structureswith high electronic conduction.
 11. The method according to claim 10,wherein the stage of heating the generator is performed before its useor at the beginning of use.
 12. The method according to claim 11,wherein the electrical voltage employed for heating is the resultant ofthe alternating component of voltage and of a direct voltage whose valueis at least equal to the open-circuit voltage of the generator.
 13. Themethod according to claim 12, wherein the said alternating and directvoltages are applied simultaneously and separately or in the form of asingle voltage resulting from their superposition.
 14. The methodaccording to claim 10, wherein the electrochemical current generator isrechargeable and the stage of heating the said generator is performedduring at least a part of the recharging cycle of the generator.
 15. Themethod according to claim 14, wherein the electrical voltage employedfor heating is the resultant of the alternating component of voltage andof a direct voltage whose value is at least equal to the nominal voltageof the charged generator.
 16. The method according to claim 15, whereinthe said alternating and direct voltages are applied simultaneously andseparately or in the form of a single voltage resulting from theirsuperposition.
 17. The method according to claim 10, wherein a number ofthin-layer electrochemical generators are combined to form a currentgenerator and wherein at least one of the said electrochemicalgenerators is employed, alternately if necessary, to produce thealternating voltage which can be employed for heating the othergenerators.
 18. The method according to claim 1, wherein the multilayerassembly comprises a thin layer of polymeric solid electrolyte orion-conducting macromolecular material intercalated between twoelectrically conductive layers forming structures with high electronicconduction and is arranged on the surface of a unit of any shape whichit is desired to heat at the surface and wherein the voltage appliedbetween the structures with high electronic conduction is solelyalternating.
 19. The method according to claim 18, wherein themultilayer assembly is formed at the surface of the unit to be heated atthe surface using painting techniques.
 20. The method according to claim19, wherein the surface of the unit to be heated at the surface has asufficient electronic conductivity to act as an electrode and whereinonto the said surface is deposited only the layer of polymeric solidelectrolyte and the corresponding electrically conductive layer isdeposited onto the latter.
 21. The method according to claim 1, whereinthe frequency of the alternating component of the electrical voltagesignal applied between the structures with high electronic conductionranges from 2 to 2,000 Hz.
 22. The method according to claim 21, whereinsaid frequency ranges from 10 to 500 Hz.
 23. The method according toclaim 1, wherein the temperature within the ion-conductingmacromolecular material is monitored in order not to exceed apredetermined temperature, the said monitoring being conducted byemploying an electrical voltage signal whose alternating component has aconstant effective value and by limiting the intensity of thealternating current generated.
 24. The method according to claim 1,wherein the temperature within the ion-conducting macromolecularmaterial is monitored in order not to exceed a predeterminedtemperature, the said monitoring being carried out by keeping constantthe intensity of the alternating current flowing in the ion-conductingmaterial and by limiting the amplitude of the alternating component ofthe electrical voltage signal.
 25. The method according to claim 6,wherein the ionizable alkali metal salt is a lithium salt.
 26. Themethod according to claim 7, wherein said polyphosphazene is one whichcarries two polyoxyethylene groups on each phosphorus atom.
 27. Themethod according to claim 6, wherein the said polymer or copolymer arepolyethers.
 28. The method according to claim 27, wherein said polyetheris an ethylene oxide polymer, a propylene oxide polymer or a copolymerof ethylene oxide and at least one cyclic ether.
 29. The methodaccording to claim 18, wherein the electrically conductive layers of themultilayer assembly arranged at the surface of the unit to be heated onits surface, each consist of a conductive deposit which is provided onone face of a paper or plastic foil, which conductive deposit is incontact with the ion-conducting macromolecular material.
 30. The methodaccording to claim 29, wherein said conductive deposit is a metaldeposit.